1. Field of the Invention
This invention relates generally to combustion systems and, more particularly, to a gas turbine engine combustion system for burning pulverized coal and for separating slag and ash from the products of combustion.
2. Description of the Prior Art
As a fuel for gas turbine engines, coal is attractive because it is available in secure and abundant quantities. Its gaseous products of combustion, however, typically are high in oxides of nitrogen (NO.sub.x) and include entrained slag and ash harmful to turbine components. Prior proposals for burning fuels with high fuel-bound nitrogen content, such as coal derived oils, have included rich-quench-lean (RQL) combustors where combustion takes place in rich and lean stages separated by quench stage in which the combustion products of the rich stage are cooled by addition of cold air. In addition, the injection of water or steam into products of combustion from a combustor has been found to have a positive effect in controlling NO.sub.x. In prior coal fueled gas turbine engines, ash removal has typically been achieved by circulating the products of combustion through a series of cyclone separators between the combustor and the turbine. A gas turbine engine combustion system according to this invention combines RQL combustion of powdered or slurried coal with a simple and efficient ash removal system using water or steam and, therefore, represents an improvement over prior coal burning combustion systems.